It is well known that some current modems operating in accordance with G.992.1 and G.992.2 standards implement a transmitter with an Inverse Fast Fourier Transform (IFFT) size greater than the one specified by the standards. These modems may implement the transmitter in either the upstream (US) or downstream (DS) direction, or both. There are many reasons that may influence this decision. For example, for an upstream channel the standard IFFT size is 64 points. However, an IFFT greater than 64 points may be justified for two reasons. A first reason is hardware symmetry with the downstream channel, since the downstream channel requires a larger Fast Fourier Transform (FFT). A second reason is ease of implementation of different Annexes of the G.992.1 and G.992.2 standards with the same data path.
Even though the use of a larger IFFT does not compromise interoperability between modems, their performance may be affected, particularly on short loops. Laboratory tests show that if the transmitter uses an IFFT other than that suggested by the standard on short loops, data rate penalties of approximately 25 to 30% are experienced.
Thus there is a need for a system and method for allowing the transmitter to use an IFFT having a size larger than that specified in the standard, while reducing data rate penalties. It is an object of the present invention to obviate or mitigate at least some of the above-mentioned disadvantages.